ADSORPTION AND DIFFUSION EFFECTS ON THE RESIDENCE TIME DISTRIBUTION OF SUBMERGED BIOFILTERS

The influence of adsorption and diffusion phenomena on the hydrodynami cs of a submerged aerated filter was studied by using stimulus-respons e techniques. Two tracers, lithium chloride and blue-dextran, and two packing materials, sepiolite and puzzolane, were used. The RTD obtaine d were analyzed by using two theoretical models: the CSTR's (Completel y Stirred Tank Reactor) in series model and the CSTR's with dead zone in series model. Experimental results confirmed that the influence of tracer adsorption on the liquid phase hydrodynamics is much smaller th an the influence of its diffusion into the packing material. The use o f different tracers brought about different results, which were interp reted according to their different diffusional behaviour. In all the e xperiments, the flow pattern approached to plug-now. The results obtai ned from the RTD analysis with both models differed in less than 25% f or the experiments done with lithium and sepiolite.